In the field of oil and gas production various activities related to wells involve the insertion of coiled tubing into the wells. Coiled tubing is typically dispended from a roll supported on a rig which inserts the tubing into the casing of the well by a coiled tubing injector head supported above the casing. When inserting the tubing, it is desirable to count the length of tubing being inserted so as to know the depth of insertion of the bottom end of the tubing.
Various types of counters are known for strand material, including cable or tubing and the like. Typical counters make use of wheels which roll along the strand material as it is dispensed. Examples of counters are found in U.S. Pat. No. 4,457,071 to Alphonso, U.S. Pat. No. 4,205,447 to Smith, U.S. Pat. No. 4,577,410 to Ritter and U.S. Pat. No. 4,481,714 to Nelson. Known systems which are suited for coiled tubing, are generally required to be installed in conjunction with the injector head or be positioned thereabove.
When counters are connected above the injector head, the counters are prone to errors due slippage on the tubing which is dirty and exposed to the environment. These counters are therefore typically unable to account for the errors due to slippage between the counting wheel and the tubing upon which the counting wheel is riding. Also, these counters are simply transported on the exterior of trucks in a manner such that they are exposed to various abuse during use and transport. Furthermore, positioning of the counter above the injector head does not take into consideration how much the tubing stretches and accordingly these types of counters are also inaccurate in addition to requiring considerable maintenance.
Counters which are supported in conjunction with the injector head typically rely on a mechanical connection to the components of the injector head which may be subject to failure due to the complexity of the mechanisms required. These types of counters are also unable to accommodate for stretch of the tubing suspended below the injector head and accordingly are also inaccurate.